Low power radio transmitter using pulse transmissions

ABSTRACT

A low power radio transmitter includes an intermediate frequency stage, signal-to-pulse conversion module, and a power amplifier. The intermediate frequency stage up-converts the frequency of a base-band digital signal into an N-bit signal at the intermediate frequency. The signal-to-pulse conversion module converts the N-bit signal at the intermediate frequency into a pulse signal of M-bits at the radio frequency. As such, the signal-to-pulse conversion module is taking an N-bit signal (e.g., an 8-bit digital signal) and converting it into an M-bit pulse signal (e.g., a 1-bit pulse stream). Accordingly, the M-bit signal at the radio frequency is essentially a square-wave, which has a peak to average ratio of zero, is subsequently amplified by the power amplifier.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to radio technology and moreparticularly to radio transmitters.

BACKGROUND OF THE INVENTION

Radio transmitters are known to include a modulator, frequencyup-converter, and a power amplifier to drive an antenna. While the basicstructure of a radio transmitter is common over various applications,the particular construction of the elements of a radio transmitter isapplication dependent. For example, an IEEE 802.11a compliant radiotransmitter includes a modulator that modulates incoming data utilizingbinary phase shift keying (BPSK), quadrature phase shift keying (QPSK),16 QAM (quadrature amplitude modulation) or 64 QAM in an orthogonalfrequency division multiplex (OFDM) manner to produce modulated data.The frequency up-converter converts the base-band modulated datadirectly, or through an intermediate frequency stage, to a radiofrequency signal having a frequency band in the 5-gigahertz range.

The power amplifier is designed to accurately amplify RF signals and todrive an antenna. An RF signal typically includes peaks that occurinfrequently and has an average value that is significantly less thanthe peak. Note that for sinusoidal based signals, the average value isgenerally measured as an rms value. For example, an IEEE 802.11acompliant RF signal has a peak occurring every 50,000–100,000 symbols,but the average value is much less, yielding a significantpeak-to-average ratio (e.g., 10–20 dB). Despite the infrequency of thepeaks that are significantly greater than average values, a poweramplifier must be designed to accurately accommodate the peak conditionsas if they were frequent events. For instance, to support an averagepower transmission of 200 milliwatts (mW), with a peak-to-average ratioof 15 dB, the power amplifier should be a 6.3 Watt amplifier. As such,the power amplifier is generally running much below its capabilities,but is designed to handle the peak conditions. Aggressive system designcan run the power amplifier at lower power so that peaks are distorted.This will increase the system error rate or require that the remainderof the system be higher performance, so that the total systemperformance is acceptable.

By having to design power amplifiers to handle signals with a largepeak-to-average ratio, the average operating point must be a sufficientdistance from the 1 dB compression point, which is approximately thepoint where the power amplifier loses linearity. Such power amplifiersconsume more power than power amplifiers that have average operatingpoints closer to the 1 dB compression point, are typically moreexpensive to construct, especially on integrated circuits, and/or haveless range of operation.

On the receiving end of a radio, the receiver includes complementarycomponents to radio transmitter. Thus, any changes made to the radiotransmitter will most likely require a complementary change to the radioreceiver.

Therefore, a need exists for improved power amplification of RF signalsto reduce cost, to reduce power consumption, and/or to increase range ofoperation such that a lower power consuming transmitter may be obtainedfor various wireless communication standards including IEEE 802.11.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic block diagram of a radio in accordancewith the present invention;

FIG. 2 illustrates a schematic block diagram of an intermediatefrequency stage of a radio transmitter in accordance with the presentinvention;

FIG. 3 illustrates a schematic block diagram of a signal-to-pulseconversion module in accordance with the present invention;

FIG. 4 illustrates a schematic block diagram of an alternatesignal-to-pulse conversion module in accordance with the presentinvention;

FIG. 5 illustrates a schematic block diagram of a detailed embodiment ofthe signal-to-pulse conversion module of FIG. 4;

FIG. 6 illustrates a schematic block diagram of another signal-to-pulseconversion module in accordance with the present invention;

FIG. 7 illustrates a schematic block diagram of a pulse width generatorin accordance with the present invention;

FIG. 8 illustrates a schematic block diagram of an alternate pulse widthgenerator in accordance with the present invention;

FIG. 9 illustrates a schematic block diagram of an alternate radio inaccordance with the present invention; and

FIG. 10 illustrates a logic diagram of a method for transmitting radiofrequency signals in accordance with the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Generally, the present invention provides a low power radio transmitterthat includes an intermediate frequency stage, signal-to-pulseconversion module, and a power amplifier. The intermediate frequencystage up-converts the frequency of a base-band digital signal into anN-bit signal at the intermediate frequency (i.e., the signal energy ofthe N-bit signal is centered at DC offset by the IF). The frequencyup-conversion includes mixing in-phase and quadrature components of thebase-band digital signal with in-phase and quadrature components of alocal oscillator. The signal-to-pulse conversion module converts theN-bit signal at the intermediate frequency into a pulse signal of M-bitat the radio frequency (i.e., the signal energy of the M-bit signal iscentered at RF). For example, the signal-to-pulse conversion module mayuse pulse-width modulation, pulse-density modulation, or pulse-positionmodulation to produce the pulse signal at the radio frequency. As such,the signal-to-pulse conversion module is taking an N-bit signal (e.g.,an 8-bit digital signal) and converting it into an M-bit pulse signal(e.g., a 1-bit pulse stream). Accordingly, the M-bit signal at the radiofrequency is essentially a square-wave, which is subsequently amplifiedby the power amplifier. With the power amplifier amplifying square-wavesignals, the peak-to-average ratio of the signal is zero. Thus, thepower amplifier may be designed to be a low-power power amplifier, havegreater operating range, and be less expensive than power amplifiersused in radio transmitters that have a peak-to-average ratio greaterthan zero.

The present invention can be more fully described with reference toFIGS. 1–10. FIG. 1 illustrates a radio 10 in accordance with the presentinvention. The radio 10 includes a transmitter section 14, receiversection 16, antenna switch 18 and an antenna 20 and may be constructedto operate in accordance with one or more wireless communicationstandards including, but not limited to, IEEE 802.11a, IEEE 802.11b,Bluetooth, advanced mobile phone services (AMPS), digital AMPS, globalsystem for mobile communications (GSM), code division multiple access(CDMA), wireless application protocols (WAP), local multi-pointdistribution services (LMDS), multi-channel multi-point distributionsystems (MMDS), and/or variations thereof. The transmitter section 14includes an intermediate frequency stage 22, a signal-to-pulseconversion module 24, a power amplifier 26, and a bandpass filter 65.

In operation, the transmitter section 14 receives a base-band digitalsignal 28 via the intermediate frequency stage 22, which converts itinto an N-bit signal 30 at an intermediate frequency. In essence, aswill be described in greater detail with reference to FIG. 2, theintermediate frequency stage 22 mixes a local oscillation with thebase-band digital signal to produce the N-bit signal 30 at theintermediate frequency. Note that N may correspond to any number from 4to 32 bits. Further note that the N-bit signal at the intermediatefrequency is essentially the baseband signal 28 with its signal energyshifted to the intermediate frequency. Still further note that theintermediate frequency is substantially less than the radio frequency,thus the N-bit signal 30 at the intermediate frequency, with respect tohigh frequencies, looks like a DC signal offset slightly by theintermediate frequency.

The signal-to-pulse conversion module 24 converts the N-bit signal 30 atthe intermediate frequency into an M-bit signal 32 at a radio frequency(i.e., the signal energy is shifted from DC offset by IF to RF). Inessence, the signal-to-pulse conversion module 24 is decreasing thenumber of bits of the signal (e.g., from eight to one) and increasingthe carrier frequency of the signal from the intermediate frequency tothe radio frequency. For example, the radio frequency may be 900megahertz for cordless telephones, 2.4 gigahertz for 802.11b orBluetooth compliant transmission, and/or 5.6 gigahertz for 802.11acompliant transmissions.

The signal-to-pulse conversion module 24 may utilize pulse-densitymodulation, pulse-width modulation or pulse-position modulation toencode the N-bit signal into an M-bit pulse signal 32. The variousembodiments of the signal-to-pulse conversion module 24 will bedescribed in greater detail with reference to FIGS. 3–8.

The power amplifier 26 amplifies the M-bit signal 32 at the radiofrequency and provides the amplified signal to the bandpass filter 65,which in turn, provides a filtered RF signal to the antenna switch 18.Correspondingly, the antenna 20 transmits the filtered M-bit signal 32at the radio frequency. The bandpass filter 65, as will be described ingreater detail with reference to FIG. 3, filters the M-bit signal 32 atRF to substantially reduce signal energy at all frequencies outside thebandwidth of the bandpass filter. This reduces the quantization noiseassociated with the M-bit signal 32 that is not near the RF carrierfrequency. As such, the input impedance of the bandpass filter 65substantially matches the impedance of the antenna at RF, but is verylarge at other frequencies. Thus, the power amplifier 26 is only drivinga significant load at the RF carrier frequency.

In addition, by pulse encoding the radio frequency signal, the poweramplifier will have a low peak-to-average ratio (e.g., zero for a 1-bitpulse encoded signal), will consume less power, will have a greaterrange of operation, and/or will be less costly than power amplifiersthat transmit RF signals having a relatively substantial peak to averageratio (e.g., greater than 10 dB). As one of average skill in the artwill appreciate, the power amplifier 26 may be implemented in a varietyof ways including, but not limited to, a Class A amplifier, a powerinverter, a transistor pull-up and/or transistor pull-down circuit, or acomparator that compares the M-bit signal at the radio frequency with areference to produce an amplified M-bit signal.

FIG. 2 illustrates a schematic block diagram of the intermediatefrequency (IF) stage 22 and corresponding frequency domainrepresentations of the signals processed by the IF stage 22. Theintermediate frequency stage 22 includes a 1^(st) mixing module 50,2^(nd) mixing module 52, summing module 54 and a local oscillator 56.The local oscillator 56 generates an in-phase intermediate frequencysignal, which is provided to the 1^(st) mixing module, and a quadratureintermediate frequency, which is provided to the 2^(nd) mixing module.

The 1^(st) mixing module also receives an in-phase component of thebase-band digital signal 28. The frequency domain representation of thein-phase component of the base-band digital signal 28 is shown adjacentto the corresponding input of the 1^(st) summing module. As shown, thein-phase component of the base-band digital signal 28 is a relativelylow frequency signal that is an even function centered about DC,indicating that it is a real signal.

The 2^(nd) mixing module 52 receives the quadrature component of thebase-band digital signal 28. The frequency domain representation of thequadrature component of the base-band digital signal 28 is shownadjacent to the corresponding input of the 2^(nd) mixing module 52. Asshown, the quadrature component of base-band digital signal 28 is an oddfunction with respect to DC and is centered around DC, indicating thatit is an imaginary signal.

The 1^(st) mixing module 50 mixes the in-phase component of thebase-band digital signal 28 with the in-phase component of the localoscillator to produce a mixed signal. The mixed signal is shown as theoutput of the 1^(st) mixing module 50. The frequency domainrepresentation of this mixed signal is shown adjacent to the output ofmixer 50. As shown, the signal is now shifted in frequency to the localoscillation frequency, or intermediate frequency.

The 2^(nd) mixing module 52 mixes the quadrature component of thebase-band digital signal 28 with the quadrature component of the localoscillator 56. The frequency domain representation of the output of the2^(nd) mixing module 52 is shown to have the odd function shifted infrequency based on the local oscillation frequency.

The summing module 54 sums the output of the 1^(st) mixing module 50with the output of the 2^(nd) mixing module 52. The resulting signal isthe N-bit signal 30 at the intermediate frequency. As shown, the signalis symmetrical about DC frequency and has a signal spectrum ofapproximately equal to twice the local oscillation frequency, i.e., theintermediate frequency. However, with respect to the radio frequency,the intermediate frequency is so small that the N-bit signal at the IFappears as a signal centered at DC, just slightly offset by theintermediate frequency. For example, if the intermediate frequency is120 MHz and the radio frequency is 5.6 GHz, the IF is approximately1/47^(th) of the RF.

FIG. 3 illustrates a schematic block diagram of an embodiment of thesignal-to-pulse conversion module 24 and corresponding frequency domainrepresentation of the signals produced thereby. The signal-to-pulseconversion module 24 includes a rate converter 58, a pulse-densitymodulator 60, and a radio frequency module 62. The radio frequencymodule 62 is operably coupled to power amplifier 26, which in turn, iscoupled to a band-pass filter 65, which may be a ceramic bandpassfilter.

The rate converter 58 receives the N-bit signal 30 at the intermediatefrequency and increases its rate to produce a rate increased K-bitsignal 64 at the intermediate frequency, where K may range from 4 to 32bits. As shown in the corresponding frequency domain representation ofthe signals, the N-bit signal 30 at the intermediate frequency iscentered about DC with signal energies at the local oscillatorfrequency. The signal spectrum 68 of the N-bit signal 30 essentiallyspans twice the local oscillation frequency.

The rate increased K-bit signal 64 at the intermediate frequency isshown to increase the signal spectrum 70 based the rate of increase, butthe signal still centered at DC offset by the intermediate frequency. Asillustrated, the signal energy is greatest at DC and is filtered in arepeating pattern due the filtering properties of the rate converter 58.In the time domain, the rate converter 58 over samples and filters theN-bit signal 30 at the intermediate frequency to produce the rateincreased K-bit signal 64 at the intermediate frequency. For example,the over sampling performed by the rate converter 58 may range from anover sampling of 8 to an over sampling of 256. In general, the rate ofthe over sampling of the rate converter 58 to produce the rate increasedK-bit signal 64 will correspond to the sampling frequency used by thepulse-density modulator 60.

The pulse-density modulator 60 converts the rate increased K-bit signal64 at the intermediate frequency into a J-bit pulse-density signal 66 atthe intermediate frequency, where J ranges from 1 to 4. In essence, thepulse-density modulator 60 is converting the digital signal into apulse-density signal. The frequency domain representation of the J-bitpulse-density signal 66 at the intermediate frequency includes thesignal energy centered at DC offset by the intermediate frequency andrepeated numerous times up to and including at the radio frequency. Inaddition, the energy of the J-bit pulse-density signal 66 includesquantization noise 72, which results from the pulse density modulationfunction.

The RF module 62 receives the J-bit pulse-density signal 66 at theintermediate frequency and up-converts the frequency to produce theM-bit signal 32 at the radio frequency. In essence, the RF module 62 isshifting the J-bit pulse density signal 66 from being centered at DC,offset by the IF, to being centered at the radio frequency. Thefrequency domain representation of the M-bit signal 32 at the radiofrequency is represented to have the signal now centered at the radiofrequency with the quantization noise spanning over various frequencies.

The power amplifier 26 amplifies the M-bit signal 32 and provides it tothe band-pass filter 65. The band-pass filter 65 filters the M-bitsignal 32 and produces RF signal 76. The frequency domain representationof the RF signal 76 is illustrated as having the quantization noisesubstantially attenuate outside of the frequency band surrounding the RFfrequency. This is generally achieved because the bandpass filter 65includes a filtering arrangement such that, at frequencies outside of asmall range around the RF carrier frequency, the filter 65 has a veryhigh impedance and, at frequencies within the small range around the RFcarrier frequency, the filter 65 has an impedance that substantiallymatches the impedance of the antenna 20.

FIG. 4 illustrates a schematic block diagram of an alternate embodimentof the signal-to-pulse conversion module 24. This embodiment includesthe rate converter 58, the pulse-density modulator 60, a 2^(nd) rateconverter 78, and the RF module 62, which are coupled to power amplifier26. The functionality of rate converter 58 and pulse-density modulator60 are as previously described with reference to FIG. 3. The rateconverter 78 is operably coupled to increase the rate of the J-bitpulse-density signal 66 to achieve a rate corresponding to the radiofrequency. The RF module 62 up-converts the frequency of the rateincrease L-bit signal 80 (where L ranges from 1 to 4) to produce theM-bit signal 32 at the radio frequency.

FIG. 5 illustrates a detailed schematic block diagram of thesignal-to-pulse conversion module 24 of FIG. 4. In this illustration,the rate converter 58 includes an over sampling module 82 that increasesthe rate of the N-bit signal 30 and further includes a filter module 84.In one embodiment, the filter module 84 is a sample and hold module,which, at a 1^(st) rate (e.g., 11X), samples and holds the over sampledN-bit signal to produce the rate increased K-bit signal 64 at theintermediate frequency.

The pulse-density modulator 60 is represented by a 2^(nd) order bandpassSigma Delta modulator. But, as one of average skill in the art willappreciate, the pulse density modulator may be implemented as a low passsigma delta modulator, third order sigma delta modulator, first ordersigma delta modulator and any other type of pulse density modulator thatquantizes an input signal into a small bit signal and pushes thequantization noise away from the signal frequency band.

In this illustration, the Sigma Delta modulator includes a summingmodule 86, a band-pass integrator module 88, a 2^(nd) summing module 90,an integrator module 92 and a divider 94. The 1^(st) summing module 86is operably coupled to subtract a feedback signal from an input signal.In this illustration, the feedback signal is representative of the J-bitpulse-density signal 66 while the input signal corresponds to the rateincreased K-bit signal 64. Note that the rate of the J-bit pulse densitysignal 66 substantially matches the rate of the rate increased K-bitsignal 64.

The band-pass integrator module 88 integrates components of the outputof the first summing module 86 within a band-pass region. The width ofthe band-pass region is dependent on the angle of 0₁ in the denominatorcomponent.

The 2^(nd) summing module 90 subtracts a scaled representation of thefeedback signal from the output of the band-pass integrator module 88.The integrator module 92 integrates the resultant of summing module 90to produce the J-bit pulse-density signal 66. Accordingly, the SigmaDelta modulator is converting a digital signal into a 1 or 2 bitpulse-density signal.

Rate converter 78 includes an over sampling module 96 that over samplesthe M-bit pulse-density signal 66 at a 2^(nd) rate (e.g., 4). The rateconverter 78 also includes a filter module 98. In one embodiment, thefilter module 98 may be a sample and hold circuit that samples and holdsthe over sampled J-bit pulse-density signal 66 to produce the rateincreased L-bit signal 80.

The RF module 62 includes a mixer 100 and a filter 102. The mixer 100mixes the rate increased L-bit signal 80 with a cosine signal, which hasa frequency corresponding to the RF frequency to produce a mixed RFsignal. The filter 102 substantially eliminates the zero of the mixed RFsignal such that few bits are needed at the output of filter 102 and,correspondingly, at the output of mixer 100. As one of average skill inthe art will appreciate, the mixing module may mix a +1, 0, −1 or 0 inplace of the cosine signal due to the over sampling and the square wavenature of the rate of the J-bit pulse-density signal 66. As such, thecircuitry implementation of the RF module is considerably less complexthan a cosine generator and a mixer. As one of average skill in the artwill also appreciate, the filter 102 may be replaced by a 1+Z⁻³ filter.

FIG. 6 illustrates a schematic block diagram of an alternate embodimentof the signal-to-pulse conversion module 24 that incorporates apulse-width modulator 110. The pulse-width modulator 110 includes adigital-to-analog converter 112, a low pass filter 114, and apulse-width generator 116. The digital-to-analog converter 112 isoperably coupled to convert the N-bit signal 30 into an analog signal118. The low pass filter 114 filters the analog signal 118 to produce afiltered analog signal 120.

The pulse-width generator 116 processes the filtered analog signal 120with respect to a pulse-width signal (e.g., a sawtooth signal) toproduce the M-bit signal 32 at the radio frequency. The power amplifier26 amplifies the M-bit signal 32, which is subsequently band-passfiltered by band-pass filter 65. The pulse-width generator 116 may beimplemented in a variety of ways including, but not limited to, thoseillustrated in FIGS. 7 and 8.

FIG. 7 illustrates a schematic block diagram of a pulse-width generator116 that includes a comparator 122 and a saw tooth generator 124. Thecomparator 122 compares the filtered analog signal 120 with a saw toothsignal generated by the saw tooth generator 124. The rate of the sawtooth signal corresponds to the radio frequency. Accordingly, as theamplitude of the filtered analog signal 120 varies, the pulse-width ofthe M-bit signal 32 varies.

FIG. 8 illustrates an alternate implementation of the pulse-widthgenerator 116 that includes the saw tooth generator 124 and a resistivenetwork 126, which is coupled to a power inverter 128. In thisembodiment, the resistive network 126 sums the filtered analog signal120 with a saw tooth signal, the resulting sum drives the power inverter128. As the magnitude of the resultant signal exceeds the thresholdvoltage for the power inverter 128, the output of the power inverter 128toggles, which is subsequently filtered via band-pass filter 65. Withthe rate of the sawtooth signal corresponding to the radio frequency,the resulting pulse width modulated signal is at RF.

FIG. 9 illustrates an alternate schematic block diagram of a radio 160.The radio 160 includes a transmitter section 164, the antenna switch 18,antenna 20 and a receiver section 166. The transmitter section 164includes a processing module 168, memory 170, the power amplifier 26,and the bandpass filter 65. The power amplifier may be implemented as aclass A amplifier, as a power inverter, as a transistor pull-up and/ortransistor pull-down circuit, or as a comparator which compares theM-bit signal with a reference signal, where the resulting comparison isan amplified version of the M-bit signal. The processing module 168 maybe a single processing device or a plurality of processing devices. Sucha processing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, and/or any device that manipulates signals (analog and/ordigital) based on operational instructions. The memory 170 may be asingle memory device or a plurality of memory devices. Such a memorydevice may be a read-only memory, random access memory, volatile memory,non-volatile memory, static memory, dynamic memory, flash memory, and/orany device that stores digital information. Note that when theprocessing module 168 implements one or more of its functions via astate machine or logic circuitry, the memory storing the correspondingoperational instructions is embedded with the circuitry comprising thestate machine or logic circuitry. The memory 170 stores, and theprocessing module 168 executes, operational instructions correspondingto at least some of the steps illustrated in FIG. 10.

FIG. 10 illustrates a logic diagram of a method for transmitting RFsignals in accordance with the present invention. The process begins atStep 180 where the frequency of a base-band digital signal isup-converted to produce an N-bit signal at an intermediate frequency.This may be done as illustrated in Steps 186–190. At Step 186, an Icomponent of a base-band digital signal is mixed with an I component ofa local oscillator, which has a period corresponding to 1 over theintermediate frequency, to produce a 1^(st) mixed signal. The processthen proceeds to Step 188 where a Q component of the base-band digitalsignal is mixed with a Q component of the local oscillation to produce a2^(nd) mixed signal. The process then proceeds to Step 190 where the1^(st) and 2^(nd) mixed signals are summed to produce the N-bit signalat the intermediate frequency.

Returning to the main flow of the diagram, the process proceeds to Step182 where the N-bit signal at the intermediate frequency is converted toan M-bit signal at an RF frequency. Note that N is greater than M whereN may range from 4 to 32 bits and M may be 1 or 2. The conversion of theN-bit signal to the M-bit signal may be done by pulse-densitymodulation, as shown at Step 192, pulse-width modulation, as shown atStep 194, or pulse-position modulation, as shown at Step 196.

If the conversion is done using pulse-density modulation, the processproceeds to Step 198–202. At Step 198, the rate of the N-bit signal atthe intermediate frequency is increased to produce a rate increasedK-bit signal at the intermediate frequency. Increasing the rate of theK-bit signal may be done by over sampling it to produce an over sampledN-bit signal. The over sampled N-bit signal may then be sampled and heldat a 1^(st) rate, which corresponds to the desired rate of increase, toproduce the rate increased J-bit signal.

The process then proceeds to Step 200 where the rate increased K-bitsignal is pulse-density modulated to produce an J-bit pulse-densitysignal, which is still at the intermediate frequency. The pulse-densitymodulation may be done by sigma delta modulation, which begins themodulation process by subtracting a feedback signal from an input signalto produce a 1^(st) resultant. The feedback signal corresponds to theJ-bit pulse-density signal and the input signal corresponds to the rateincreased K-bit signal. The sigma delta modulation continues byband-pass integrating components of the 1^(st) resultant in a band-passregion to produce a band-pass integrated signal. The sigma deltamodulation then continues by subtracting a 2^(nd) feedback signal fromthe band-pass integrated signal to produce a 2^(nd) resultant. The2^(nd) feedback signal corresponds to a scaled version of the J-bitpulse-density signal. The sigma delta modulation then continues byintegrating the 2^(nd) resultant to produce the J-bit pulse-densitysignal.

After pulse-density modulating the K-bit signal to produce the J-bitpulse density signal, the process proceeds to Step 202 where thefrequency of the J-bit pulse-density signal is increased from theintermediate frequency to the radio frequency. Note that prior toincreasing the frequency, the rate of the M-bit pulse-density signal maybe further increased.

If the conversion of the N-bit signal into the M-bit pulse-densitysignal is done using pulse-width modulation, the processing proceeds toStep 204–206. At Step 204, the N-bit signal is converted into an analogsignal. The process then proceeds to Step 206 where the analog signal islow pass filtered to produce a filtered analog signal. The process thenproceeds to Step 208 where the M-bit signal at the radio frequency isgenerated as a pulse-width modulated signal based on a comparison of thefiltered signal with a pulse-width reference signal (e.g., a saw toothsignal).

Having converted the N-bit signal at the intermediate frequency into anM-bit signal at an RF frequency, the process proceeds to Step 184 wherethe M-bit signal at the radio frequency is amplified. Once the signal isamplified, it may be band-pass filtered at the radio frequency andsubsequently provided to an antenna for transmission.

The preceding discussion has presented a transmitter and receiver thatutilize pulse-encoded signals to transceive data via an RF communicationpath. By utilizing pulse-encoded signals, the signals have asubstantially square-wave waveform. As such, the peak-to-average ratiois approximately zero. Accordingly, power amplifiers within thetransmitter section may be designed for a peak-to-average ratio of zero,which allows them to be more efficient, have greater operating range, besmaller—thus consuming less integrated real estate—and therefore areless costly. As one of average skill in the art will appreciate, otherembodiments may be derived from the teaching of the present inventionwithout deviating from the scope of the claims.

1. A radio transmitter comprises: intermediate frequency stage operablycoupled to up-convert frequency of a baseband digital signal into anN-bit signal at an intermediate frequency; signal to pulse conversionmodule operably coupled to convert the N-bit signal at the intermediatefrequency into an M-bit signal at a radio frequency, wherein N isgreater than M, and wherein the signal to pulse conversion moduleincludes: rate converter operably coupled to increase rate of the N-bitsignal at the intermediate frequency to produce a rate increased K-bitsignal at the intermediate frequency; pulse density modulator operablycoupled to convert the rate increased K-bit signal at the intermediatefrequency into an J-bit pulse density signal at the intermediatefrequency; second rate converter operably coupled to increase rate ofthe J-bit pulse density signal at the intermediate frequency to producea rate increased L-bit signal at the intermediate frequency; and radiofrequency module operably coupled to increase frequency of the rateincreased L-bit signal at the intermediate frequency into the M-bitsignal at the radio frequency; and power amplifier operably coupled toamplify the M-bit signal at the radio frequency.
 2. The radiotransmitter of claim 1, wherein the intermediate frequency stage furthercomprises: first mixing module operably coupled to mix an in-phasecomponent of the baseband digital signal with an in-phase intermediatefrequency signal to produce a first mixed signal; second mixing moduleoperably coupled to mix a quadrature component of the baseband digitalsignal with a quadrature intermediate frequency signal to produce asecond mixed signal; and summing module operably coupled to sum thefirst and second mixed signals to produce the N-bit signal at theintermediate frequency.
 3. The radio transmitter of claim 1 furthercomprises: the rate converter including: oversampling module operablycoupled to oversample the N-bit signal at the intermediate frequency toproduce an oversampled N-bit signal; and sample and hold module operablycoupled to sample and hold, at a first rate, the oversampled N-bitsignal to produce the rate increased K-bit signal at the intermediatefrequency; and the second rate converter including: second oversamplingmodule operably coupled to oversample the J-bit pulse density signal atthe intermediate frequency to produce an oversampled M-bit signal; andsecond sample and hold module operably coupled to sample and hold, at asecond rate, the oversampled M-bit signal to produce the rate increasedL-bit signal at the intermediate frequency.
 4. The radio transmitter ofclaim 1, wherein the pulse density modulator further comprises: bandpasssigma delta modulator that includes: first summing module to subtract afeedback signal from an input signal to produce a first resultant,wherein the feedback signal is representative of the J-bit pulse densitysignal at the intermediate frequency and the input signal isrepresentative of the rate increased K-bit signal at the intermediatefrequency; bandpass integrator module operably coupled to integratecomponents of the first resultant in a bandpass region to produce abandpass integrated signal; second summing module operably coupled tosubtract a second feedback signal from the bandpass integrated signal toproduce a second resultant, wherein the second feedback signal isrepresentative of a scaled version of the J-bit pulse density signal atthe intermediate frequency; and integrator module operably coupled tointegrate the second resultant to produce the J-bit pulse density signalat the intermediate frequency.
 5. The radio transmitter of claim 1,wherein the power amplifier comprises at least one of: comparatoroperably coupled to compare the M-bit signal at the radio frequency witha reference to produce an amplified M-bit signal; class A amplifieroperably coupled to amplify the M-bit signal at the radio frequency;inverter operably coupled to invert the M-bit signal at the radiofrequency; and transistor pull-up and pull-down circuit operably coupledto amplify the M-bit signal at the radio frequency.
 6. The radiotransmitter of claim 1 further comprises: ceramic bandpass filteroperably coupled to bandpass filter an output of the power amplifier toproduce a bandpass M-bit square wave signal; and an antenna operablycoupled to transmit the bandpass M-bit square wave signal.
 7. A methodfor radio frequency signal transmissions, the method comprises:up-converting frequency of a baseband digital signal into an N-bitsignal at an intermediate frequency; converting the N-bit signal at theintermediate frequency into an M-bit signal at a radio frequency,wherein N is greater than M, and wherein the converting of the N-bitsignal at the intermediate frequency into the M-bit signal at the radiofrequency includes: increasing rate of the N-bit signal at theintermediate frequency to produce a rate increased K-bit signal at theintermediate frequency; pulse density modulating the rate increasedK-bit signal at the intermediate frequency into an J-bit pulse densitysignal at the intermediate frequency; increasing rate of the J-bit pulsedensity signal at the intermediate frequency to produce a rate increasedL-bit signal at the intermediate frequency; and increasing frequency ofthe rate increased L-bit signal at the intermediate frequency into theM-bit signal at the radio frequency; and amplifying the M-bit signal atthe radio frequency.
 8. The method of claim 7, wherein the up-convertingthe frequency of the baseband signal further comprises: mixing anin-phase component of the baseband digital signal with an in-phaseintermediate frequency signal to produce a first mixed signal; mixing aquadrature component of the baseband digital signal with a quadratureintermediate frequency signal to produce a second mixed signal; andsumming the first and second mixed signals to produce the N-bit signalat the intermediate frequency.
 9. The method of claim 7 furthercomprises: increasing rate of the N-bit signal at the intermediatefrequency includes: oversampling the N-bit signal at the intermediatefrequency to produce an oversampled N-bit signal; and sampling andholding, at a first rate, the oversampled N-bit signal to produce therate increased K-bit signal at the intermediate frequency; andincreasing rate of the J-bit pulse density signal at the intermediatefrequency includes: oversampling the J-bit pulse density signal at theintermediate frequency to produce an oversampled M-bit signal; andsampling and holding, at a second rate, the oversampled M-bit signal toproduce the rate increased L-bit signal at the intermediate frequency.10. The method of claim 7, wherein the pulse density modulating furthercomprises: subtracting a feedback signal from an input signal to producea first resultant, wherein the feedback signal is representative of theJ-bit pulse density signal at the intermediate frequency and the inputsignal is representative of the rate increased K-bit signal at theintermediate frequency; bandpass integrating components of the firstresultant in a bandpass region to produce a bandpass integrated signal;subtracting a second feedback signal from the bandpass integrated signalto produce a second resultant, wherein the second feedback signal isrepresentative of a scaled version of the J-bit pulse density signal atthe intermediate frequency; and integrating the second resultant toproduce the J-bit pulse density signal at the intermediate frequency.11. The method of claim 7 further comprises: bandpass filtering theamplified M-bit signal at the radio frequency to produce a bandpassM-bit square wave signal; and providing the bandpass M-bit square wavesignal to an antenna for transmission.
 12. An apparatus for radiofrequency signal transmissions, the apparatus comprises: processingmodule; and memory operably coupled to the processing module, whereinthe memory includes operational instructions that cause he processingmodule to: up-convert frequency of a baseband digital signal into anN-bit signal at an intermediate frequency; convert the N-bit signal atthe intermediate frequency into an M-bit signal at a radio frequency by:increasing rate of the N-bit signal at the intermediate frequency toproduce a rate increased K-bit signal at the intermediate frequency;pulse density modulating the rate increased K-bit signal at theintermediate frequency into an J-bit pulse density signal at theintermediate frequency; increasing rate of the J-bit pulse densitysignal at the intermediate frequency to produce a rate increased L-bitsignal at the intermediate frequency; and increasing frequency of therate increased L-bit signal at the intermediate frequency into the M-bitsignal at the radio frequency; wherein N is greater than M; and amplifythe M-bit signal at the radio frequency.
 13. The apparatus of claim 12,wherein the memory further comprises operational instructions that causethe processing module to up-convert the frequency of the baseband signalby: mixing an in-phase component of the baseband digital signal with anin-phase intermediate frequency signal to produce a first mixed signal;mixing a quadrature component of the baseband digital signal with aquadrature intermediate frequency signal to produce a second mixedsignal; and summing the first and second mixed signals to produce theN-bit signal at the intermediate frequency.
 14. The apparatus of claim13, wherein the memory further comprises operational instructions thatcause the processing module to: increase rate of the N-bit signal at theintermediate frequency by: oversampling the N-bit signal at theintermediate frequency to produce an oversampled N-bit signal; andsampling and holding, at a first rate, the oversampled N-bit signal toproduce the rate increased K-bit signal at the intermediate frequency;and increase rate of the J-bit pulse density signal at the intermediatefrequency by: oversampling the J-bit pulse density signal at theintermediate frequency to produce an oversampled M-bit signal; andsampling and holding, at a second rate, the oversampled M-bit signal toproduce the rate increased L-bit signal at the intermediate frequency.15. The apparatus of claim 13, wherein the memory further comprisesoperational instructions that cause the processing module to pulsedensity modulate by: subtracting a feedback signal from an input signalto produce a first resultant, wherein the feedback signal isrepresentative of the J-bit pulse density signal at the intermediatefrequency and the input signal is representative of the rate increasedK-bit signal at the intermediate frequency; bandpass integratingcomponents of the first resultant in a bandpass region to produce abandpass integrated signal; subtracting a second feedback signal fromthe bandpass integrated signal to produce a second resultant, whereinthe second feedback signal is representative of a scaled version of theJ-bit pulse density signal at the intermediate frequency; andintegrating the second resultant to produce the J-bit pulse densitysignal at the intermediate frequency.
 16. The apparatus of claim 12,wherein the memory further comprises operational instructions that causethe processing module to: bandpass filter the amplified M-bit signal atthe radio frequency to produce a bandpass M-bit square wave signal; andprovide the bandpass M-bit square wave signal to an antenna fortransmission.
 17. A radio transmitter comprises: intermediate frequencystage operably coupled to up-convert frequency of a baseband digitalsignal into an N-bit signal at an intermediate frequency; signal topulse conversion module operably coupled to convert the N-bit signal atthe intermediate frequency into an M-bit signal at a radio frequency,wherein N is greater than M, the signal to pulse conversion moduleincluding: a rate converter operably coupled to increase rate of theN-bit signal at the intermediate frequency to produce a rate increasedK-bit signal at the intermediate frequency; pulse density modulatoroperably coupled to convert the rate increased K-bit signal at theintermediate frequency into an J-bit pulse density signal at theintermediate frequency; and radio frequency module operably coupled toincrease frequency of the J-bit pulse density signal at the intermediatefrequency into the M-bit signal at the radio frequency; and poweramplifier operably coupled to amplify the M-bit signal at the radiofrequency.
 18. The radio transmitter of claim 17, wherein theintermediate frequency stage further comprises: first mixing moduleoperably coupled to mix an in-phase component of the baseband digitalsignal with an in-phase intermediate frequency signal to produce a firstmixed signal; second mixing module operably coupled to mix a quadraturecomponent of the baseband digital signal with a quadrature intermediatefrequency signal to produce a second mixed signal; and summing moduleoperably coupled to sum the first and second mixed signals to producethe N-bit signal at the intermediate frequency.
 19. The radiotransmitter of claim 17, wherein the power amplifier comprises at leastone of: comparator operably coupled to compare the M-bit signal at theradio frequency with a reference to produce an amplified M-bit signal;class A amplifier operably coupled to amplify the M-bit signal at theradio frequency; inverter operably coupled to invert the M-bit signal atthe radio frequency; and transistor pull-up and pull-down circuitoperably coupled to amplify the M-bit signal at the radio frequency. 20.The radio transmitter of claim 17 further comprises: ceramic bandpassfilter operably coupled to bandpass filter an output of the poweramplifier to produce a bandpass M-bit square wave signal; and an antennaoperably coupled to transmit the bandpass M-bit square wave signal. 21.A method for radio frequency signal transmissions, the method comprises:up-converting frequency of a baseband digital signal into an N-bitsignal at an intermediate frequency; converting the N-bit signal at theintermediate frequency into an M-bit signal at a radio frequency,wherein N is greater than M, and wherein the converting of the N-bitsignal at the intermediate frequency into the M-bit signal at the radiofrequency includes: increasing rate of the N-bit signal at theintermediate frequency to produce a rate increased K-bit signal at theintermediate frequency; pulse density modulating the rate increasedK-bit signal at the intermediate frequency into an J-bit pulse densitysignal at the intermediate frequency; and increasing frequency of theJ-bit pulse density signal at the intermediate frequency into the M-bitsignal at the radio frequency; and amplifying the M-bit signal at theradio frequency.
 22. The method of claim 21, wherein the up-convertingthe frequency of the baseband signal further comprises: mixing anin-phase component of the baseband digital signal with an in-phaseintermediate frequency signal to produce a first mixed signal; mixing aquadrature component of the baseband digital signal with a quadratureintermediate frequency signal to produce a second mixed signal; andsumming the first and second mixed signals to produce the N-bit signalat the intermediate frequency.
 23. The method of claim 21 furthercomprises: bandpass filtering the amplified M-bit signal at the radiofrequency to produce a bandpass M-bit square wave signal; and providingthe bandpass M-bit square wave signal to an antenna for transmission.24. An apparatus for radio frequency signal transmissions, the apparatuscomprises: processing module; and memory operably coupled to theprocessing module, wherein the memory includes operational instructionsthat cause he processing module to: up-convert frequency of a basebanddigital signal into an N-bit signal at an intermediate frequency;convert the N-bit signal at the intermediate frequency into an M-bitsignal at a radio frequency by: increasing rate of the N-bit signal atthe intermediate frequency to produce a rate increased K-bit signal atthe intermediate frequency; pulse density modulating the rate increasedK-bit signal at the intermediate frequency into an J-bit pulse densitysignal at the intermediate frequency; and increasing frequency of theJ-bit pulse density signal at the intermediate frequency into the M-bitsignal at the radio frequency; wherein N is greater than M, and amplifythe M-bit signal at the radio frequency.
 25. The apparatus of claim 24,wherein the memory further comprises operational instructions that causethe processing module to up-convert the frequency of the baseband signalby: mixing an in-phase component of the baseband digital signal with anin-phase intermediate frequency signal to produce a first mixed signal;mixing a quadrature component of the baseband digital signal with aquadrature intermediate frequency signal to produce a second mixedsignal; and summing the first and second mixed signals to produce theN-bit signal at the intermediate frequency.
 26. The apparatus of claim24, wherein the memory further comprises operational instructions thatcause the processing module to: bandpass filter the amplified M-bitsignal at the radio frequency to produce a bandpass M-bit square wavesignal; and provide the bandpass M-bit square wave signal to an antennafor transmission.